Equations for Exam One

Question 1

C2Cl3F3 normal boiling point of 47.6c calculate the energy required to convert 35.0g of C2Cl3F3 from a liquid 10.00c to a gas 105.00c?
Hvap C2Cl3F3 = 27.49 KJ/mol
Spec heat cap. Liquid = .91 J/gxK
Spec heat cap. gas = .67 J/gxK

Answer 1

10.00 to 47.6 q1 = MCAT
evaporate at 47.6 q2 = AHvap x mol
47.6 to 105 q3 = MCAT

Total Energy = q1 + q2 + q3

Answer = 7.7 KJ

Question 2

CH3NIO2 Vapor pressure is 344 torr at -25c and boiling point of -6.9c. What is the AHvap for CH3NIO2?
R = 8.314 J/mol-K

Answer 2

USE In(p2/p1)=
-AHvap/R(1/T2-1/T1)

Answer = 23 KJ/mol

Question 3

PO in group 16 (6A) and is radioactive. Only element with structure based on simple cubic unit cell. If density of PO is 9.142 g/cm3, calculate approximate atomic radius for PO.

Answer 3

Use L3; L=2r

use stoic to get PO in grams.

then use v=m/d to get volume

then use L3;L=2r

convert cm to pm

Answer = 168pm

Question 4

One brand of laundry bleach is an aqueous solution containing 4.55% sodium hypochlorite (NaOCl) by mass. What is the molarity of this solution? (assume density 1.02g/mL)

Answer 4

% mass to molarity = mol/L

find mol of NaOCl

then find L using 1.02g g/mL with also 100g of the solution

Plug in numbers

Answer = .623M

Question 5

Dissolve 155.2g of glucose (C6H12O6) in water to make 1L of solution. If solution density is 1.062g/mol, what is molal concentration of the solution?

Answer 5

Use Molality = Moles of solute/mass of solvent

calculate moles of C6H12O6 using grams

mass= v x d

Answer = .950M

Question 6

What is the molarity of .792m of C6H12O6, if the solution density is 1.16g/mL? molar mass = 180.16g

Answer 6

Find volume of solution using .792mol and 1Kg of solvent

mass of solute = .792mol x 180.16g/mol = 142.68g
mass of solvent = 1 Kg = 1000g

add two totals to get mass of solution

use m/d to get volume.

then use M = mol/L

Answer = .804M

Question 7

Dissolve 20.2mL CH3OH in 100.0mL of H2O. Final volume is 118mL. What is the mole fraction of CH3OH? Densities = CH3OH = .782g/mol
H2O= 1g/mol

Answer 7

First find mass and mol of CH3OH
Then find mass and mol of H2O
Use mole fraction equation= XCH3OH= CH3OH mol / CH3OH mol + H2O mol

Answer = .0816

Question 8

Dissolve 155.2g of C6H12O6 in water to make 1L of solution. If solution density is 1.062g/mL, what is the mole fraction of glucose in the solution?

Answer 8

First find the mol of C6H12O6

then mass of solvent=H2O

then mol of H2O

Put in mole fraction equation= mole of solute/ mol of solution

Answer= .01683

Question 9

Dissolve 155.2g of C6H12O6 in water to make 1L of solution. If solution density is 1.062g/mL, what is the mole fraction of water in the solution?

Answer 9

Find mol for C6H12O6
and mol for H2O

Put the necessary numbers in to get H2O mole fraction with the H2O at the top.

Answer=.9832

Question 10

Potassium nitrate lattice energy is -163.8 Kcal/mol and heat of hydration is -155.5 Kcal/mol. How much KNO3 has to dissolve in water to absorb 1.00x10^2 KJ of heat? Use 4.184 KJ = 1Kcal

Answer 10

Use equation AHsoln=
-(AH LE) + AH HYD

Then convert Kcal/mol to KJ/mol

Then use the number to find the mass of KNO3

A= 2.9x10^2g

Question 11

At 25.0°C the Henry’s Law constant (kH) for N2O gas in water
is 0.025 M/atm. Calculate the mass in grams of N2O gas that
can be dissolved in 1450. mL of water at 25.0°C and a N2O
partial pressure, PN2O = 2.42 atm.

Answer 11

Use: SN2O = kH x PN2O

Then find moles using the molarity formula

Use that number x the molar mass of N2O

A=3.9g

Question 12

62.1 g of glycol (HOCH2CH2OH) in 250.
g of water. What is the vapor pressure of water over
the solution at 30 oC? (The VP of pure H2O is 31.8
mmHg).

Question 13

At a certain temperature the vapor pressure of pure
chloroform, CHCl3, is measured as 0.45 atm. Suppose a
solution is prepared by mixing 93.7 g of CHCl3 and 99.9 g of
acetyl bromide, CH3COBr. Calculate the partial pressure of
chloroform vapor, PCH3Cl , above this solution.

Answer 13

Use PCH3Cl = XCH3Cl x PoCH3Cl to solve for PCH3Cl

First find the moles of CHCl3 and CH3COBr

Add both of the moles together

Multiply total with CH3Cl moles

use that number with .45 atm

A= .22 atm

Question 14

Dissolve 7.55 g of glycol, C22HH66OO22 in 85.7 mL ofin 85.7 mL of
ethanol (0.798 g/mL). What is the boiling point of the solution?

Question 15

Dissolve 62.1 g of glycol, C22HH66OO22 (1.00 mol) in 250
g of water. What is the bp of the solution?

Question 16

A particular solvent has a freezing point of 53.0c and a
freezing point depression constant of 7.10. What is the
freezing point of the solution containing 5.85 g of napthalene,
CC1010HH88, (molar mass = 128.2 g/mol) dissolved in 33.5 g of the
solvent?

Question 17

Calculate the osmotic pressure of a solution containing 24.6 g
glycerin (C3H8O3) in 250.0 mL of aq. soln @ 298 K;
molar mass C3H8O3 = 92.09 g/mol.